The present invention relates to apparatus and method for encoding and decoding digital video data and, more particularly, to apparatus and method for encoding and decoding digital video data which enable low and high-speed reproduction of variable rate encoded digital video data, and also to a record medium having stored thereon variable rate encoded digital video data in a particular data structure which enables the low and high-speed reproduction thereof.
As is known, MPEG compressed digital video data includes intraframe encoded digital video data (xe2x80x9cI-framesxe2x80x9d) and interframe encoded digital video data including forward predictive encoded data (xe2x80x9cP-framesxe2x80x9d) and bi-directionally predictive encoded data (xe2x80x9cB-framesxe2x80x9d). Generally, an I-frame is decoded without using data of other frames, but P and B-frames are decoded utilizing other frames.
A bit stream of MPEG compressed digital video data generally is divided into groups of pictures (GOPs), and each GOP begins with an I-frame. When digital video data is MPEG compressed at a fixed rate, for example, when the frame pattern of the GOP is fixed, I-frames periodically occur in the bit stream at known positions thereof and, thus, high speed reproduction of the video data by reproducing only I-frames therein is possible since the general position of each I-frame is known. However, when digital video data is MPEG compressed at a variable rate (e.g., the frame pattern of a GOP is variable) I-frames do not occur in the bit stream at known intervals thereof and, thus, high speed reproduction by reproducing only I-frames is difficult.
One technique for accomplishing higher than normal speed reproduction of MPEG compressed digital video data is to record in each sector that includes an I-frame at the beginning of a GOP therein a flag which indicates the existence of the I-frame, and to record in that sector the sector addresses (i.e., positions) of adjacent sectors that include I-frames therein. Therefore, a relatively slow search speed can be accomplished by reproducing adjacent I-pictures in the bit stream.
One problem with the above-discussed technique is its general inability to reproduce video data from a record medium in high-speed searching modes wherein it is desirable to successively reproduce I-frames occurring at relatively high intervals of time, for example, every 1, 2, 4, etc. seconds, in the bit stream.
Therefore, it is an object of the present invention to provide apparatus and method for encoding and decoding digital video data which overcome the shortcomings of the above-discussed reproducing technique.
Another object of the present invention is to provide apparatus and method for encoding and decoding digital video data which is operable to achieve low and high speed reproduction of compressed digital video data.
A further object of the present invention is to provide a recording and reproducing technique which operate to achieve both high and low speed reproduction of variable rate compressed digital video data.
An additional object of this invention is to provide a technique which allows for the reproduction of I-frames temporally occurring at predetermined constant intervals of time.
Still another object of the present invention is to provide a record medium having compressed digital video data stored thereon which is reproducible at low and high search speeds.
A still further object of this invention is to provide for the low and high speed reproduction of compressed digital still image and audio data.
In accordance with one embodiment of the present invention, apparatus and method operate to variable rate encode digital video data (i.e., intraframe and interframe encode), identify a selected plurality of entry points of the encoded video data which represent respective locations of video frames that occur at predetermined intervals of time (e.g. 1, 2 and 4 seconds) in the video picture, generate entry point data that identifies the positions of the entry points, add the entry point data to the encoded video data, and record the encoded video data having the entry point data added thereto on a record medium.
As one aspect of the present invention, the entry point data identifies entry points of intraframe encoded frames that occur at the predetermined intervals of time in the video picture.
As a feature of this aspect, the entry point data identifies an entry point of the intraframe encoded frame that is located nearest in time to the frame that occurs at one of the predetermined time intervals when that frame is not an intraframe encoded frame.
As another aspect of this invention, respective entry point data is added to each intraframe encoded frame that identifies entry points of intraframe encoded frames that occur at predetermined intervals of time before and after the intraframe encoded frame to which the respective entry point data is added.
In accordance with another embodiment of the present invention, apparatus and method operate to reproduce from a record medium variable rate encoded digital video data which represents a plurality of successive video frames and which includes therein entry point data that identifies positions of locations of video frames that occur at predetermined intervals of time in the video picture, extract the entry point data from the reproduced data, store the extracted entry point data in a memory, control the reproduction of the encoded data in accordance with entry point data that is stored in the memory so as to reproduce a particular video frame, and variable rate decode the reproduced data to produce decoded video data.
As one aspect of this embodiment, the reproduced data includes intraframe and interframe encoded frames and each reproduced intraframe encoded frame includes respective entry point data that identifies entry points of intraframe encoded frames that occur at the predetermined intervals of time from the intraframe encoded frame to which the respective entry point data is included. After the reproduction of one intraframe encoded frame, one of the intraframe encoded frames that is identified by the entry point data included in the reproduced intraframe encoded frame then is reproduced.
In accordance with a further embodiment of the present invention, a record medium comprises a plurality of variable length video data areas in which variable encoded digital video data is stored, wherein the encoded digital video data includes a plurality of intraframe and interframe encoded frames each of which is stored in a respective one of the video data areas, and a plurality of entry point data areas in which entry point data are stored, wherein the entry point data identifies positions of entry points of the encoded digital video data which represent respective locations of video data areas in which intraframe encoded frames that occur at predetermined intervals of time in the video picture are stored.
In accordance with yet another embodiment of the present invention, apparatus and method operate to variable rate encode digital still image and audio data, identify entry points that represent locations of the still images in the encoded data, generate entry point data that identifies positions of the identified entry points in the encoded data, add the entry point data to the encoded data, and record the encoded data having the entry point data added thereto on a record medium.
In accordance with yet a further embodiment of the present invention, apparatus and method operate to reproduce from a record medium variable rate encoded digital still image data that includes therein entry point data that identifies positions of entry points of the encoded data which represent respective locations of still images in the encoded data, extract the entry point data from the reproduced encoded data, store the extracted entry point data in a memory, control the reproduction of the encoded data in accordance with entry point data stored in the memory to reproduce an encoded still image, and variable rate decode the reproduced encoded still image to produce a decoded still image.